#define _CRT_SECURE_NO_WARNINGS  1
#include <stdio.h>
//1/1-1/2+1/3-1/4
int main()
{
	double n,m,i;
	n = 0;
	m = 1;
	i = 1;
	while (m<=100)
	{
		n = n + (1 / m) * i;
		m+=1;
		i = -i;
	}
	printf("%lf", n);
	return 0;
}